What’s the difference between a positive shower pump and a negative shower pump?
In simple terms – if your shower head is positioned lower than your cold water storage tank, you can use a positive shower pump. If the shower head is higher than the water tank (e.g. a loft conversion), a negative pump is needed.
Where a gravity flow of water is in excess of 0.6 litres per minute, this is known as a Positive Head condition. In this situation, a positive shower pump can be used.
A Negative Head condition is when the gravity flow is water is less than 0.6 litres per minute. The most common reasons being an outlet installed higher than the cold water tank level, or because of a restrictive valve. In these conditions a negative shower pump must be used.
Negative shower pumps will work in both positive and negative head conditions. So for example, in a situation when there is a shower head above and below the water tank level; one negative shower pump can be used for both, as shown in the diagram below.